Sun Tracking Solar Power System

Introduction

Sources of energy

With growing development, there arises subsequent need of energy for every part of human life. The main source of energy is nature, which provides several sources like the fossil fuels. The natural resources can be classified into non renewable and renewable sources of energy.

Non renewable sources of energy like coal, oil, natural gas are mostly used, but cannot be replenished. Also factors such as global warming, continuing fuel rise create hindrance in using of these sources of energy.

Henceforth the only way is to use renewable sources of energy, which can be replenished and replaced. Examples are wind energy, solar energy, thermal energy.

Sun as Source of Energy

Nuclear fusion in the active core of the sun produce and inner temperature of 107K and an inner radiation flux of uneven spectral distribution. This inner radiation is absorbed in the outer passive layers which are heated to about 5800K. This radiation generates light energy in form of photons which carry large amount of energy and momentum. These photons can either be deflected or can absorbed during their journey from the sun to the earth.

The earth receives solar radiation power of approximately 1.73*1014 KW. This continuously received power integrates to a total energy of 5.46*1021MJ per year. Thus solar energy is the most relevant source of energy required to cater to the growing demands of mankind.

There are three different ways to gather this energy, based on the type of collector:

Flat-plate collectors are the more commonly used type of collector today. They are arrays of solar panels arranged in a simple plane.

Focusing collectors are essentially flat-plane collectors with optical devices arranged to maximize the radiation falling on the focus of the collector. These are currently used only in a few scattered areas. Solar furnaces are examples of this type of collector.

Passive collectors are completely different from the other two types of collectors. The passive collectors absorb radiation and convert it to heat naturally, without being designed and built to do so.

Solar Panels

Out of these flat plate collectors are most widely used. An example being a solar panel.

A solar panel is a cluster of solar cells arranged in matrix. These panels can gather power between 10 to 300W.

A solar cell is a two layered semiconductor device which is used to absorb the radiation. It works on the principle of photovoltaic, which implies generation of voltage through incident light. When light falls on the layers, it excites the electrons, causing them to jump from one layer to another, forming an electrical charge.

The typical solar power receiving system consists of the following parts

Solar Panel- To gather the power.

Inverter- To convert the received DC power to AC.

Battery- To store the received DC power.

Mounting of Solar Panels

One of the major constraints in the use of solar panels is in the way they are mounted so as to receive the maximum light energy from the sun.

The factors which affect the output or the efficiency of the solar panel are as follows:

Direction: Incase of the location being Northern Hemisphere, the panels should face due north and the location being Southern Hemisphere, the panels should face due south.

Tilt or Orientation: Solar Panels must have a tilt equal to the latitude of their location. As the tilt of the earth rotation changes, the solar panels need to be adjusted to get maximum light.

Type of surface: A broader surface is mostly preferred, as it receives maximum amount of sunlight.

To make efficient mounting of the panels, so that they receive adequate sunlight, devices called Trackers are used which point the panels towards the earth.

There are two types of trackers:

a. Passive Tracker:

Passive trackers use a system whereby a liquid moves as it is heated by the sun and is used to move the panel, automatically returning to the correct position for the morning. It basically consists of two tube tanks placed at sides of the solar panel such that in case of Panel not being aligned with the sun, the liquid in the tanks gets unevenly heated causing a pressure difference. This pressure difference in turn causes the liquid to move towards the tank with low temperature. Thus as the liquid level fluctuates between the two tanks, the shift in weight causes gravity to rotate the tracker along with the orientation of the Sun. They are less expensive and require no electrical appliances and require less maintenance. However conventional light sensing mechanism may not prove accurate during cloudy days and also they are not efficient.

b. Active Tracker:

An Active Tracker usually consists of motors like a Servo Motor or a Stepper motor to rotate the panel. Ideally solar radiation strikes the panel at 90⁰ angles. The motor maintains the panel at that angle, so as to receive the maximum radiation. The control of the motor can be done in either of the two ways. One way is using an electronic system to calculate the astronomical position of the sun at the particular location and accordingly rotate the solar panel at an orientation perpendicular to the sun at preset time intervals. Another of control is using a sensor arrangement to sense the brightness in the sky and accordingly rotate the panel at right angles to the orientation of the sun.

Application of the Above Method

The stepper motor is controlled using the microcontroller 8051, through the relay driver IC ULN2003A. It consists of the low power panel on its shaft and provides a rotation of 0 to 180⁰ rotations in steps of 5 secs interval each. This rotation of the stepper motor corresponds to earth’s rotation around the sun, which accounts for 180⁰ change in the earth’s direction with respect to the sun. The stepper motor is programmed so as to provide 90⁰ rotation in most of the time.